(1) Field of the Invention
This invention relates to heat and solvent sensitive recording materials on which information can be recorded to make transparencies for projection of information or for making photographic negatives for reproduction and to the process for making transparencies for recording or reproduction using the recording materials.
More particularly, the invention relates to heat and solvent sensitive recording materials of the type in which an opaque layer is coated on a transparent support and in which the opaque layer can be transparentized by writing on the opaque layer with a solvent for the pigment component of the opaque layer or by application of heat to the opaque layer.
(2) Discussion of the Prior Art
U.S. Pat. No. 3,014,301 to W. Grupe relates to a recording material referred to as recording chart or chart medium, for use in recording units with a heated or a pressure stylus, and/or a pen containing a solvent. The chart medium is made with a transparent film backing upon which is deposited a white, opaque coating which is heat, pressure and solvent sensitive. The coating is formed from an unstable solution of nitrocellulose in acetone (a solvent) and zylol (a non-solvent). The whiteness and opacity results from the acetone evaporating first leaving a high percentage of xylol and nitrocellulose in solution, from which the nitrocellulose is precipitated as a white solid. The chart is transparentized by "printing" the opaque layer with a solvent such as Cellosolve or carbitol acetate from a solvent dispensing pen. A transparent dye can be added to the solvent to form transparent lines color-dyed but photographically transparent so that it may be used as a negative for photographic reproduction or as a positive transparency for projection onto screens or other medium. The chart medium can be used, for example, for preparing graphs with conventional pen-operated machines.
A similar sheet recording material which is sensitive to pressure is disclosed by R. S. Ives in U.S. Pat. No. 2,962,382, except that water replaces xylol as the high boiling non-solvent and various film-forming polymeric materials such as cellulose acetate, ethyl cellulose and polyethyl methacrylate are disclosed in addition to nitrocellulose as the opaque material. This patent also discloses methyl ethyl ketone and methyl alcohol, in addition to acetone as suitable volatile solvents for the polymeric materials. However, the opaque coatings taught by Ives require large amounts of surfactant or a combination of surfactant and waxy lubricant to produce useful pressure-sensitive materials.
Other related heat, solvent and/or pressure sensitive recording papers are described in U.S. Pat. No. 2,299,991--W. F. Kallock; U.S. Pat. No. 3,147,062--W. E. Glenn, Jr.,; U.S. Pat. No. 3,265,524--I. P. Echeagaray; U.S. Pat. No. 3,180,752--A. E. Bollinger, et al., U.S. Pat. No. 3,320,089--E. G. Bourgeois; U.S. Pat. No. 3,642,475--Vraneken, et al.
While the recording materials described in the above patents provide satisfactory transparencies, in many cases they suffer from the drawback that it is very difficult to obtain uniform opaque coatings by depositing a layer of polymeric material from an unstable mixture of volatile solvent and high-boiling nonsolvent. Precise control of the rate of evaporation of the volatile solvent is necessary to obtain opaque coatings and uniformity to the opacity over the entire surface. Reproducibility from sheet to sheet is also difficult. Furthermore, the degree of opacity with the polymer/solvent/non-solvent systems of these patents is generally not as high as desireable for good contrast between the transparent film backing sheet and the opaque coating layer.
In the applicant's copending application Ser. No. 912,546, novel opaque coatings are described that can be prepared from an aqueous dispersion of finely divided particles of a styrene resin with a transparent film-forming binder, particularly, polyvinylidene chloride (PVDC) and that when such an opaque coating is deposited on a transparent backing sheet, positive transparencies for projection of images of the transparent "writing"or negative transparencies for photographic reproduction can be obtained by application of a solvent for the styrene resin particles (pigment) to the opaque coating. The prior application is directed to an information recording kit for making transparencies for projection of information or for making photographic negatives for reproduction, the kit including the opaque recording material (film), writing liquid (solvent) and writing means (e.g., pen), whereby when writing liquid is applied to the opaque layer, according to a pattern of information, the opaque layer becomes photographically transparent (transparent to visible light) according to the pattern. The prior application is also directed to a method for writing (recording information) for projection, display or reproduction by transparentizing the film by applying the writing solvent to the opaque layer.
The prior application also taught to incorporate one or more fluorochloroalkanes having boiling points greater than 0.degree. C. to the writing liquid to overcome problems associated with toxicity, flammablility, and malodor of typical solvents for the styrene resin opacifying pigment particles, as well as, in many cases, to improve the effectiveness, e.g., speed, of the writing liquid.
While satisfactory transparencies are available on the market, they are limited to the heat-sensitive type using a heat recording apparatus and special originals with the image zones capable of absorbing infrared light. Furthermore, known heatsensitive recording materials, such as sold by the Minnesota Mining and Manufacturing Company (3M) under the designation "Thermofax Transparency 528", give transparencies whose transparent zones have a too high haze value (as defined below) for some applications. When using such known transparencies with a writing liquid, the traces obtained are so bad that in practice they cannot be used with a solvent writing means.
Furthermore, such materials cannot be used successively with heat and solvent. When used with the "Thermofax Secretary 45" of the 3M Company, the original is placed on the top of the transparencies, in intimate contact with the sensitive coating. To have a readable image, the opaque coating must be placed on the overhead projector with the transparent backing sheet facing the operator. It is, thus, impossible to write on this material during the projection on the screen.